Cobalt Additive Lab Report

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In order to investigate the effect of cobalt additive on the phosphate coatings, the surface morphology of these coatings was evaluated. Scanning electron microscopy images for the samples containing cobalt additive are shown in Fig. 1. Based on the illustrated pictures (1-a), phosphate coating without additive has more cracks than the other samples. By adding the additive, the amount of crack in the coating’s structure decreased; the lowest amount of cracks was observed for sample containing 3g/lit ion cobalt (Figure 1-d). The structure of phosphate crystals based on the obtained results is mainly in the form of plate and mud. Phosphate coatings containing additive have a more plate texture than phosphate coatings without additives, so that the most plate-shaped structure was observed for sample containing 3g/lit ions of cobalt. Therefore, changing the amount of plate-shaped structure based on surface morphology leads to an increase in the size of phosphate crystals for specimens containing cobalt additive [27]. By adding the cobalt additive, the phosphate crystals formed on the zinc get more uniform and contain less porosity. The densest coating of the phosphate coating samples was obtained with 3g/lit ions of cobalt. However, the excessive addition of additive (4…show more content…
The size of the phosphate crystals for the phosphate coating consisting of 1 and 3 g/lit Co is 50 and 38 nm, respectively. Thus increasing the amount of additive by increasing the germination points reduces the size of phosphate crystals. However, the addition of 3 g/lit Co to the coating, in comparison with the phosphate coating with 2 and 4 g/lit Co additives, increases the size of the phosphate crystals and the thickness of the coating, and can be effective in improving the corrosion resistance of the

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